to Developmental Biology
Figure 14-7 Diagram of the upper limb of three species: human, bird, and bat. Despite the superficially dissimilar appearance of the human arm and hand, the avian wing, and the bat wing, the similarity in their underlying bone structure and functionality reveals the homology of the forelimbs of all three species. In contrast, the two superficially similar wings in the bird and bat are analogous, not homologous structures. Although both the bird and bat wings are used for flying, they are constructed quite differently and did not evolve from a winglike structure in a common ancestor. See Sources & Acknowledgments.